<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <style>
        .outer{
            width: 100%
        }
        .left{
            width: 200px;
            display: inline-block;
            background-color: red
        }
        .right{
            display: inline-block;
            background-color: blue
        }
    </style>
</head>
<body>
        <div class="outer">
            <div class="left">left</div>
            <div style=" width:calc(100% - 200px)">right</div>
        </div>
</body>
</html>